This sample chapter from the best-selling Adobe ColdFusion 8 Web Application Construction Kit, Volume 2: Application Development takes you through many of the advanced features of ColdFusion Components.

The previous chapter covered the basics of ColdFusion Components: how to create them, use them, store data in them, and make them persist. But you can do a lot more with ColdFusion Components. This chapter presents many of the more advanced features of ColdFusion Components, including inheritance, security, type checking, and serialization. This chapter also covers a few features of components new to ColdFusion 8.

Specifying Data Types and Type Checking

As mentioned in the previous chapter, methods in ColdFusion Components can return types through the use of the returntype attribute of cffunction. Consider this example:

<cffunction name="listFilms" returnType="query" output="false">

Here, the method must return a variable with a data type of query. Any other return type would cause an error. For example, it might make sense to return a value of the Boolean false because no valid query could be returned, but that would throw an error. Instead, you'd want to return an empty query or throw a custom error.

You can also specify data types as arguments for methods. In any cfargument, you can specify the type that your method must return (just as with cfparam). This specification can prevent you from having to create a lot of custom error-handling code in your application to check the data types of arguments passed in, and it also helps in introspection (covered in more depth later in this chapter and also in Chapter 26, "Building Reusable Components"). In addition, the cfproperty tag allows you to document for introspection local variables and define a type that the arguments will have for self-documentation.

Any value that can be parsed into a date. Note that POP dates (see the ParseDateTime function) and time zones are not accepted, but simple timestamps and ODBC formatted dates and times are accepted.

GUID

The argument must be a UUID or GUID of the form xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx where each x is a character representing a hexadecimal number (0-9A-F)

Numeric

Integer or float.

Query

ColdFusion Query Result Set.

String

ColdFusion String simple data type.

Struct

ColdFusion Struct complex data type.

UUID

The argument must be a ColdFusion UUID of the form xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx where each x is a character representing a hexadecimal number (0-9A-F).

variableName

A string formatted according to ColdFusion variable naming conventions (a letter, followed by any number of alphanumeric characters or underscores).

Void

Does not return a value.

If anything else is specified as a return type, ColdFusion processes it as returning a component for which properties have been defined. This technique allows components to define complex types for Web services. Chapter 67, "Using Server-Side HTTP and FTP," in Vol. 3, Advanced Application Development, discusses this feature in depth. Typically, though, the standard data types will suffice.

Our Actors master-detail application has two data-access actions—currently each one a cfquery on each of the two CFML pages. Our Actors component, then, will have two methods, each defined with a <cffunction> tag. <cffunction> uses the same introspection attributes as <cfcomponent>: displayname and hint.

Another attribute, output, can be set to "no" if your function doesn't write anything out. This works like a virtual <cfsilent> tag, and causes all the whitespace in a pure code function to be discarded by ColdFusion. If you set it to "yes", your function works as if the entire function is wrapped in a <cfoutput> tag, and anything in number signs (#) will be interpreted as ColdFusion variables. If you don't specify the output attribute, it works like any other ColdFusion code—you need to either wrap output in <cfoutput> or use the WriteOutput() function.

Finally, there are two additional arguments you can use when defining components in ColdFusion: roles, used to secure functionality by user; and access, used to hide implementation details. We'll come back to these later in this chapter.

Using the GetMetaData() Function

You can dump a component with cfdump. For example, you can dump FilmRotationCFC.cfc from the previous chapter as shown here:

As you can see, the dump shows the component's methods and instance data. This data can be useful to your code. ColdFusion provides a means to programmatically examine an instance of a component to get this data: the getMetaData() function. The getMetaData() function returns a structure containing the same information that you can see in the HTML view of a component that cfdump provides.

There are two syntaxes for using the getMetaData() function. From outside of a component, pass the function a reference to the component object. Within a component, pass the function the component's own scope keyword THIS. So, for example, the code

With this data, you could produce component HTML documentation in whatever form you wish, simply by accessing the information in the structure. This approach can be useful when you want to check the properties of a component that's been passed into a function or verify whether a method is implemented in it. This specification is demonstrated in Listing 27.1.

Listing 27.1. getMetaData.cfm—Display Data Using getMetaData()

<!---
getMetaData.cfm
Demonstrate use of getMetaData() function
--->
<!--- instantiate the FilmRotationCFC object into cfcfilmRotation --->
<cfobject component="FilmRotationCFC" name="cfcFilmRotation">
<!--- now get the metadata, into the ourMetaData function --->
<cfset ourMetaData = getMetaData(cfcFilmRotation)>
<cfoutput>
<!--- Show the displayName and size; we could also show the hint,
path, etc. --->
<h3>Welcome to the #ourMetaData. Name#!</h3>
Enjoy our #arrayLen(ourMetaData.functions)# functions:
<ul>
<!--- loop through and show each function's name; could also show
hint, parameters array, etc. but let's keep it simple. --->
<cfloop index="thisFunction" from="1" to="#arrayLen(ourMetaData.functions)#">
<li>#ourMetaData.functions[thisFunction]. Name#</li>
</cfloop>
</ul>
</cfoutput>